Abstract
We provide a review of the enoplid suborder Trefusiina Siddiqi, 1983, based on morphological considerations and analyses of new and published 18S rDNA sequences. We also describe Halanonchus scintillatulus Leduc sp. nov. from the Hauraki Gulf, northern New Zealand, as well as females of Trefusialaimus idrisi Leduc, 2013 from the continental slope of New Zealand. We show for the first time that the structure of the female reproductive system of Trefusialaimus Riemann, 1974 consists of two opposed and outstretched ovaries, an unusual feature for the Enoplida. The Trefusiina did not form a monophyletic group in the 18S rDNA phylogeny due to the placement of Lauratonema Gerlach, 1953 and Trefusialaimus sequences well away from the main Trefusiina clade. However, due to generally weak Maximum Likelihood support values, we refrain from changing the classification of these taxa until more comprehensive analyses can be conducted. Our phylogenetic analysis supports the inclusion of the Trischistomatidae Andrássy, 2007 within the Trefusiina, meaning that all of the enoplid suborders now include at least some terrestrial/freshwater representatives. The Trefusiina currently comprises five families, 14 genera and 92 valid species.
Highlights
Knowledge of phylogenetic relationships within the nematode order Enoplida Filipjev, 1929 has progressed substantially in the last two decades, largely as a result of molecular phylogenetic analyses of European Journal of Taxonomy 661: 1–45 (2020)18S rDNA sequences
We provide a review of the enoplid suborder Trefusiina Siddiqi, 1983, based on morphological considerations and analyses of new and published 18S rDNA sequences
We provide the first record of the genus Halanonchus from the New Zealand region, describe the female reproductive system of Trefusialaimus for the first time and provide the first molecular sequences for this genus
Summary
Knowledge of phylogenetic relationships within the nematode order Enoplida Filipjev, 1929 has progressed substantially in the last two decades, largely as a result of molecular phylogenetic analyses of European Journal of Taxonomy 661: 1–45 (2020)18S rDNA sequences. The Alaimina Clark, 1961 was moved to the Enoplida by De Ley & Blaxter (2002) from the Dorylaimida Pearse, 1942, where it was previously classified by Lorenzen (1981), the Campydorina Jairajpuri, 1983 was placed with the Enoplida by Mullin et al (2003), and the order Trefusida Lorenzen, 1981 was ranked as a suborder within the Enoplida by De Ley & Blaxter (2004) based on analyses presented by Rusin et al (2001) These and other changes have led to the current division of Enoplida, which comprises seven suborders: the Enoplina Chitwood & Chitwood, 1937, Trefusiina Siddiqi, 1983, Tripyloidina De Coninck, 1965, Oncholaimina De Coninck, 1965, Ironina Siddiqi, 1983, Campydorina Jairajpuri, 1983 and Alaimina (De Ley & Blaxter 2004). Several other SSU phylogenies and molecular studies have shown a close relationship between Trischistoma, Tripylina and the Enoplida, and the family Trefusiidae in particular (Holterman et al 2006; Meldal et al 2007; Zhao & Buckley 2009; van Megen et al 2009; Zhao et al 2012)
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